Central Pit Research Articles

Seismic evidence and formation mechanism of gas hydrates in the Zhongjiannan Basin, Western margin of the South China Sea

An analysis of 3D seismic data from the Zhongjiannan Basin in the western margin of the South China Sea (SCS) reveals seismic evidence of gas hydrates and associated gases, including pockmarks, a bottom simulating reflector (BSR), enhanced reflection (ER), reverse polarity reflection (RPR), and a dim amplitude zone (DAZ). The BSR mainly surrounds Zhongjian Island, covering an area of 350 km2 in this 3D survey area. The BSR area and pockmark area do not match each other; where there is a pockmark developed, there is no BSR. The gas hydrate layer builds upward from the base of the stability zone with a thickness of less than 100 m. A mature pockmark usually consists of an outside trough, a middle ridge, and one or more central pits, with a diameter of several kilometers and a depth of several hundreds of meters. The process of pockmark creation entails methane consumption. Dense faults in the study area efficiently transport fluid from large depths to the shallow layer, supporting the formation of gas hydrate and ultimately the pockmark.

Evolution of Occator Crater on (1) Ceres

Abstract The dwarf planet Ceres (diameter 939 km) is the largest object in the main asteroid belt. Recent investigations suggest that Ceres is a thermally evolved, volatile-rich body with potential geological activity, a body which was never completely molten but possibly differentiated into a rocky core, an ice-rich mantle, and which may contain remnant internal liquid water. Thermal alteration and exogenic material infall contribute to producing a (dark) carbonaceous chondritic-like surface containing ammoniated phyllosilicates. Here we report imaging and spectroscopic analyses of Occator crater derived from the Framing Camera and the Visible and Infrared Spectrometer onboard Dawn. We found that the central bright spot (Cerealia Facula) of Occator is ∼30 Myr younger than the crater itself. The central spot is located in a central pit which contains a dome that is spectrally homogenous, exhibiting absorption features that are consistent with carbonates. Multiple radial fractures across the dome indicate an extrusive formation process. Our results lead us to conclude that the floor region was subject to past endogenic activity. Dome and bright material in its vicinity formed likely due to a long-lasting, periodic, or episodic ascent of bright material from a subsurface reservoir rich in carbonates. Originally triggered by an impact event, gases, possibly dissolved from a subsurface water/brine layer, enabled material rich in carbonates to ascend through fractures and be deposited onto the surface.

Resident-performed neodymium:YAG laser posterior capsulotomy

ObjectiveTo investigate the outcomes of resident-performed Nd:YAG laser posterior capsulotomy. DesignCombined retrospective and prospective study. ParticipantsPatients (N = 301) who underwent Nd:YAG capsulotomy by ophthalmology residents at Rassoul Akram Hospital, Tehran, Iran. MethodsAssessment of visual outcomes and complications and the results of second- and third-year residents. ResultsIn the retrospective arm, 131 eyes of 129 patients were enrolled. Mean best-corrected visual acuity (BCVA) improved significantly from 1.15 ± 0.26 to 0.54 ± 0.39 logMAR (p < 0.001). Mean intraocular pressure (IOP) before capsulotomy and at the final visit was 13.1 ± 2.34 mm Hg and 13.6 ± 2.17 mm Hg, respectively (P = 0.30). Retinal detachment occurred in 2 eyes (1.5%). No case of intraocular lens decentration or endophthalmitis was detected. In the prospective arm on 173 eyes of 172 patients, mean pre-YAG BCVA was 1.14 ± 0.25 logMAR and increased to 0.51 ± 0.37 logMAR after surgery (p < 0.001). There was no significant difference between pre-laser IOP measurements compared with the 1-month IOP measurements (P = 0.32). The postoperative changes in mean BCVA and IOP between the second- and third-year residents were not significant; however, the applied laser power, the number of laser spots, rate of incomplete capsulotomies, and the amount of total and central laser-induced IOL pits were significantly higher among the second-year residents. ConclusionsResident-performed capsulotomy appears to be effective with a low complication profile. Despite the lower levels of surgical skills, second-year residents could achieve good visual outcomes. The laser parameters and IOL-related complications improved with increasing surgical experience.

Novel Catalytically-Inactive PII Metalloproteinases from a Viperid Snake Venom with Substitutions in the Canonical Zinc-Binding Motif.

Snake venom metalloproteinases (SVMPs) play key biological roles in prey immobilization and digestion. The majority of these activities depend on the hydrolysis of relevant protein substrates in the tissues. Hereby, we describe several isoforms and a cDNA clone sequence, corresponding to PII SVMP homologues from the venom of the Central American pit viper Bothriechis lateralis, which have modifications in the residues of the canonical sequence of the zinc-binding motif HEXXHXXGXXH. As a consequence, the proteolytic activity of the isolated proteins was undetectable when tested on azocasein and gelatin. These PII isoforms comprise metalloproteinase and disintegrin domains in the mature protein, thus belonging to the subclass PIIb of SVMPs. PII SVMP homologues were devoid of hemorrhagic and in vitro coagulant activities, effects attributed to the enzymatic activity of SVMPs, but induced a mild edema. One of the isoforms presents the characteristic RGD sequence in the disintegrin domain and inhibits ADP- and collagen-induced platelet aggregation. Catalytically-inactive SVMP homologues may have been hitherto missed in the characterization of snake venoms. The presence of such enzymatically-inactive homologues in snake venoms and their possible toxic and adaptive roles deserve further investigation.

Mobile soak pits improve spray team mobility, productivity and safety of PMI malaria control programs

In the President’s Malaria Initiative (PMI)-funded Africa Indoor Residual Spraying Project (AIRS), end-of-day clean-up operations require the safe disposal of wash water resulting from washing the exterior of spray tanks and spray operators’ personal protective equipment. Indoor residual spraying (IRS) programs typically use soak pits - large, in-ground filters – to adsorb, filter and then safely degrade the traces of insecticide found in the wash water. Usually these soak pits are permanent installations serving 30 or more operators, located in a central area that is accessible to multiple spray teams at the end of their workday. However, in remote areas, it is often impractical for teams to return to a central soak pit location for cleanup. To increase operational efficiency and improve environmental compliance, the PMI AIRS Project developed and tested mobile soak pits (MSP) in the laboratory and in field applications in Madagascar, Mali, Senegal, and Ethiopia where the distance between villages can be substantial and the road conditions poor. Laboratory testing confirmed the ability of the easily-assembled MSP to reduce effluent concentrations of two insecticides (Actellic 300-CS and Ficam VC) used by the PMI AIRS Project, and to generate the minimal practicable environmental “footprint” in these remote areas. Field testing in the Mali 2014 IRS campaign demonstrated ease of installation and use, resulted in improved and more consistent standards of clean-up, decreased transportation requirements, improved spray team working conditions, and reduced potential for operator exposure to insecticide.

Fluvial erosion as a mechanism for crater modification on Titan

There are few identifiable impact craters on Titan, especially in the polar regions. One explanation for this observation is that the craters are being destroyed through fluvial processes, such as weathering, mass wasting, fluvial incision and deposition. In this work, we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on Titan. We find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as Cassini, given enough time and a large enough erosion rate. A difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in Titan’s crater population. Fluvial erosion also removes central peaks and fills in central pits, possibly explaining their infrequent occurrence in Titan craters. Although many craters on Titan appear to be modified by aeolian infilling, fluvial modification is necessary to explain the observed impact crater morphologies. Thus, it is an important secondary modification process even in Titan’s drier equatorial regions.

Stocks of soil organic carbon in forest ecosystems of the Eastern Usambara Mountains, Tanzania

An inventory of soil organic carbon (SOC) stocks to 100-cm depth was carried out at four pedologically comparable forest sites in the Amani Nature Reserve (Eastern Usambara Mountains, NE Tanzania). Three plots at primary tropical submontane forests and one plot at a secondary forest derived from selective cutting were sampled. The aim was to quantify the SOC stocks including the spatial variation, and to put the findings into a pedological context. At each site, a combined approach was applied with auger samples taken to 40-cm depth (topsoil) at eight points (10cm depth intervals) surrounding a central soil pit. The subsoil was sampled at 40–100cm depth in the soil pit, accompanied by a detailed soil description and classification according to FAO and WRB. In addition, soil analysis comprised a set of chemical and physical parameters. According to WRB, the soils belonged to the reference groups Acrisols and Alisols, depending on the method used for estimating clay-related potential cation exchange capacity. The SOC stocks to 100-cm depth ranged between 16.9 and 22.4kgCm−2 (mean 19.7kgCm−2). The SOC stock at the secondary forest (20.2kgCm−2) did not differ from those of the primary forest plots. In all profiles the subsoil contributed to the SOC stocks to 100-cm depth, whereas the contribution of the forest floor was small. The variation of SOC stocks between the forest sites may be explained by ‘old’ land-use and/or differences in soil chemical parameters controlling SOC stabilization. The SOC stocks appear to be related to the amounts of poorly crystallized Fe- and Al-oxides. The mechanisms and potentials for SOC sequestration are, however, unclear and merit further detailed study. Our inventory of SOC under forest represents a suitable baseline for the assessment of SOC stock changes after land-use conversion to agriculture on typical soils of the humid tropics.

Evidence for an explosive origin of central pit craters on Mars

Kilometer-scale pits are nested in the centers of many impact craters on Mars as well as on icy satellites. They have been inferred to form in the presence of a water–ice rich substrate; however, the process(es) responsible for their formation is still debated. Previous models invoke origins by either explosive excavation of potentially water-bearing crustal material, or by subsurface drainage of meltwater and/or collapse. If explosive excavation forms central pits, pit-derived ejecta should be draped around the pits, whereas internal collapse should not deposit significant material outside pit rims. Using visible wavelength images from the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) instruments and thermal infrared images from the Odyssey Thermal Emission Imaging System (THEMIS) instrument, we conducted a survey to characterize, in detail, the global population of central pits in impact craters ⩾10km in diameter. We specifically examined the morphology and thermophysical characteristics of the pits for evidence of pit ejecta. Our analysis of thermal images suggests that coarse-grained materials are distributed proximally around many central pits on the floors of their host craters. The decrease in average grain size with distance from pit rims is consistent with pit-derived ejecta. These observations and interpretations better support an explosive origin for central pits on Mars than they do an origin of subsurface meltwater drainage and collapse of the overlying substrate. A major weakness to previous explosive central pit formation models is the inability for them to form pits late enough in the impact process to be preserved. To address this, we present an alternative “melt contact model” where a central uplift brings ice-bearing substrate into contact with impact melt to generate steam explosions and excavate central pits during the impact modification stage. Theoretical calculations show that more than enough thermal energy is available via impact melt from the host crater to form central pits by steam explosions, and such explosions would require only a modest amount (2–6% by volume) of uplifted water–ice. We therefore propose that central pits on Mars could have formed explosively by the interaction of impact melt and subsurface water–ice.

Müller cell alignment in bird fovea: possible role in vision.

Birds which possess high visual acuity, such as eagles and falcons, are known to have retinas with a deep conically curved central foveal pit. There have been different attempts to explain the importance of this particular shape of the fovea in visual resolution. Recently, the function of Müller cells as "light fibers" was discovered, showing how the endfeet of Müller cells trap the light and then transfer it to a single cone photoreceptor. Here we describe how the endfeet of Müller cells line the walls of the foveal pit in the Pied Flycatcher, and how the Müller cell body extends its processes towards individual cones, forming machinery that could allow for light transfer from the pit wall to the photoreceptor layer alongside the pit. We describe how this construction may send an image from the fovea to the cones, and also, how the angular positioning of Müller cells, being optical extensions of the cones, has the advantage of being much denser than on a flat or slightly curved fovea. We, therefore, suggest that this type of optic fiber alignment can be used as a novel type of "amplifying array" that simply increases the amount of megapixels at the photoreceptor cell layer.

A comparison between the occlusal morphology of virtually reconstructed posterior crowns and natural molars.

This study was performed to evaluate the occlusal morphologic similarities between virtually reconstructed full crowns and original natural teeth. A total of 40 stone cast sets with untreated first molars (22 maxillary and 18 mandibular) were scanned and saved as three-dimensional virtual models. The 40 first molars on the stone casts were prepared for all-ceramic restorations, scanned again, and virtually restored with a full veneer crown using a biogeneric tooth algorithm. For comparison of original and virtually restored teeth, orthographic measurements were performed on the cusp tip configurations from the central pits. The measurements were compared using the concordance correlation coefficient (CCC). For maxillary molars, the ranges of CCC were 0.040 to 0.566 in linear, 0.127 to 0.509 in area, and -0.114 to 0.327 in angular measurements. For mandibular molars, the ranges of CCC were 0.104 to 0.555 in linear, 0.183 to 0.597 in area, and 0.030 to 0.396 in angular measurements. The reproducibility of automatic occlusal construction was relatively low. There is a need for improvement in the biogeneric tooth algorithms to enhance the accuracy of restoring to the original occlusal tooth form in cases of full veneer crown preparation.

Craters on comets

This paper reviews the observations of crater-like features on cometary nuclei. We compare potential crater sizes and morphologies, and we discuss the probability of impacts between small asteroids in the Main Belt and a comet crossing this region of the Solar System. Finally, we investigate the fate of the impactor and its chances of survival on the nucleus.We find that comets do undergo impacts although the rapid evolution of the surface erases most of the features and make craters difficult to detect. In the case of a collision between a rocky body and a highly porous cometary nucleus, two specific crater morphologies can be formed: a central pit surrounded by a shallow depression, or a pit, deeper than typical craters observed on rocky surfaces.After the impact, it is likely that a significant fraction of the projectile will remain in the crater. During its two years long escort of comet 67P/Churyumov–Gerasimenko, ESA׳s mission Rosetta should be able to detect specific silicates signatures at the bottom of craters or crater-like features, as evidence of this contamination.For large craters, structural changes in the impacted region, in particular compaction of material, will affect the local activity. The increase of tensile strength can extinct the activity by preventing the gas from lifting up dust grains. On the other hand, material compaction can help the heat flux to travel deeper in the nucleus, potentially reaching unexposed pockets of volatiles, and therefore increasing the activity. Ground truth data from Rosetta will help us infer the relative importance of those two effects.

Sustainability, culture and personal responsibility

The conclusion of the 2011 Nobel meeting in Stockholm on Sustainability (http://globalsymposium2011.org/) was unambiguous: we need a change in collective mindset to achieve our vision and goal. As an anthropologist, therefore I ask myself: ‘‘What might be the barriers to such a change?’’ About 15 years ago, I visited the highlands of Papua New Guinea as a guest to my wife, who was doing research there. In these parts, because the climate is wet and cold at an elevation of over 2000 m, people’s lives focus on a fire that is maintained at all times in a central hearth pit. It serves to heat the dwelling and to cook. In one village, we observed that the inhabitants had devised a simple and very effective tool to help in cooking: a piece of bamboo had been heated over the fire and bent to create a pair of pincers much like one finds in our culture to serve salad. Whenever the food (mainly sweet potato and taro) was cooked, they would take the tubers out of the fire with this tool. Surprisingly, in a neighboring village, not more than a day’s walk distant, they did not have such a tool, and thus they burnt their fingers every time they had to fetch food from the fire. As the people in both villages interact regularly, I asked myself: ‘‘Why don’t the people in the second village adopt the very efficient and easy-to-make tool invented in the first?’’ I think the answer lies in the fact that a cultural or technical tradition, which we commonly define in our Western scientific culture by what is included in it (tools, know-how, institutions, etc.), is actually defined not by its content, but by the things the people concerned have never thought about—their ‘blind spots’, the questions they have never asked themselves, and to which they therefore have not devised any answers. The boundaries of the known are inherently the things not known, those never seen as interesting or relevant. Why is that important in the sustainability debate? First of all, because it explains to a large extent why it has proven impossible to deal with GHG emissions by means of a worldwide, ‘top-down’ treaty such as the Kyoto treaty or the UNFCCC. Every nation, every region, has a different perception of what needs to be done and how to do it. Whereas it was possible for nations in a phase of plenty to S. E. van der Leeuw (&) School of Human Evolution and Social Change, Arizona State University, Phoenix, USA e-mail: vanderle@asu.edu

Pit B or not Pit B? The pitfall array is the question

Pitfall trapping is a long established method for trapping terrestrial vertebrates globally. Many variations in bucket and drift fence arrays are used. Recent survey guidelines have been published for Queensland and the Northern Territory. In Queensland a “T” pattern is recommended, and we used data collected over five years to assess whether the use of this array, with the addition of a central bucket (Pit B), results in more captures, particularly in the central bucket. A total of 263 sites representing 1052 bucket samples were examined and the differences in capture abundance in bucket location was tested using analysis of variance. Pitfall bucket location significantly affected the captures of Dasyuridae, Muridae, Agamidae, Pygopodidae, Scincidae (P<0.1), and mean abundance was highest in the central Pit B except for Agamidae. There was also significant variation in abundance across habitat type for these families, excluding Dasyuridae, but including Gekkonidae. We conclude that having a central bucket where drift fences join can increase trap success, and this is a function of effective trapping area (i.e. catchment of animal activity and length of drift fence per bucket). Increased captures may have some relationship to habitat type (i.e. small mammals more abundant in grassland habitat). Though this particular array has some benefits in increasing trap success, the use of multiple survey techniques is recommended for any thorough fauna inventory.

Multiple climate shifts in the Southern Hemisphere over the past three centuries based on central Antarctic snow pits and core studies

AbstractBased on the results of geochemical and glaciological investigations in snow pits and shallow cores, regional stack series of air temperature in central Antarctica (in the southern part of Vostok Subglacial Lake) were obtained, covering the last 350 years. It is shown that this parameter varied quasi-periodically with a wavelength of 30–50 years. The correlation of the newly obtained record with the circulation indices of the Southern Hemisphere (SH) shows that the central Antarctic climate is mainly governed by the type of circulation in the SH: under conditions of zonal circulation, negative anomalies of temperature and precipitation rate are observed, whereas the sign of the anomalies is positive during meridional circulation. In the 1970s the sign of the relationship between many climatic parameters changed, which is likely related to the rearrangement of the climatic system of the SH. The data suggest that during the past 350 years such events have taken place at least five times. The stable water isotope content of the central Antarctic snow is governed by the summer temperature rather than the mean annual temperature, which is interpreted as the influence of ‘postdepositional’ effects.

Multiple climate shifts in the Southern Hemisphere over the past three centuries based on central Antarctic snow pits and core studies

Multiple climate shifts in the Southern Hemisphere over the past three centuries based on central Antarctic snow pits and core studies

慶州蘿井の八角形建物址における柱配置計画に関する研究

This study is about the octagonal building of GYEONGJU NAJONG, the remains of a ritual facility of ancient Shilla Dynasty. The purpose of this study is to examine the column arrangement of the octagonal building, and reveal the determinant factors for column arrangement by reviewing the sequential processes in building the facility.The results are as follows : the octagonal building was designed with special structure that internal structure is rotated against external column arrangement. Difference in the number of columns between inside and outside was caused by restrictions on the scale of the inner and outer circumference. And it induced rotation of the internal structure for the external column array. The circumference of internal and external column of the octagonal building was defined to include the core portion of predecessor facility, consisting of the central pit and the six pits.

A global inventory of central pit craters on the Moon: Distribution, morphology, and geometry

The origin of central pit craters on the Moon has long been an enigma, and a primary reason is that their geographic distribution and morphometric characteristics were unknown. We investigated a global inventory of lunar central pit craters using high-resolution image and topography data obtained from the Lunar Reconnaissance Orbiter. 56 certain and 35 probable central pit craters are found on both the lunar maria and highlands. The certain pit craters are ∼9–57km in diameter. The average diameter ratio between the central pits and their parent craters is ∼0.12 and the average depth/diameter ratio for the central pits is ∼0.072. With irregular-shaped rims, the central pits have conical profiles and some have flat floors. The central pits occur on both crater floors and central peaks. The floor pits are generally larger, deeper, and with more irregular shape compared with summit pits. Both the summit and floor pit craters have formed in every lunar stratigraphic epoch from Nectarian to Copernican. Target properties of background terrains affect the morphology and size of central pits, but they do not determine whether or not a central pit forms during a cratering event. The lunar central pits may have formed by deformation of central peaks caused by some mechanical processes during or soon after the cratering process of their parent craters.

Reprint of: Impact craters with ejecta flows and central pits on Mercury

Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.

Impact craters with ejecta flows and central pits on Mercury

Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.

A new archosauriform reptile from the Middle Triassic (Ladinian) of Germany

Numerous well-preserved skeletal remains of a distinctive armoured archosauriform reptile from the Lower Keuper (Erfurt Formation; Middle Triassic: Ladinian: Longobardian) of Baden-Württemberg (Germany) represent a new taxon, Jaxtasuchus salomoni gen. et sp. nov. The dermal armour of Jaxtasuchus comprises transverse rows of four rectangular osteoderms each in the cervical, dorsal and caudal regions, with the individual plates closely resembling those of Doswellia kaltenbachi from Carnian strata in North America. The long and low maxilla of Jaxtasuchus held at least 15 teeth. The labial and lingual surfaces of the tall, only slightly recurved crowns of the maxillary teeth bear distinct vertical ridges and smooth mesial and distal carinae. The cervical region of the vertebral column is long. Phylogenetic analysis places Jaxtasuchus as the sister taxon to Doswellia in Doswelliidae sensu Desojo et al. (2011). Doswelliidae is diagnosed by the coarsely reticulate, incised ornamentation of osteoderms composed of central regular pits of subequal size and contour, and a mostly smooth anterior articular lamina on each osteoderm. The discovery of Jaxtasuchus confirms that Doswelliidae had a wide palaeogeographical distribution during the latter half of the Triassic.http://www.zoobank.org/urn:lsid:zoobank.org:pub:4A400628-07F3-4D1B-9CA8-336C379721FA